document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=170724>Question 170724</A>: <I><SPAN STYLE=\"word-break: break-all;\">  I need help with this problem. I am not sure what formula to use.<BR>\n" );
document.write( "An aquarium tank can hold 540 liters of water. There are two pipes that can be used to fill the tank. The first pipe alone can fill the tank in 60 minutes. The second pipe can fill the tank in 90 minutes by itself. When both pipes are working together, how long does it take them to fill the tank?  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #126029 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=126029\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> An aquarium tank can hold 540 liters of water. <BR>\n" );
document.write( "There are two pipes that can be used to fill the tank. The first pipe alone can fill the tank in 60 minutes. <BR>\n" );
document.write( "The second pipe can fill the tank in 90 minutes by itself. <BR>\n" );
document.write( "When both pipes are working together, how long does it take them to fill the tank? <BR>\n" );
document.write( "-------------<BR>\n" );
document.write( "1st pipe DATA:<BR>\n" );
document.write( "Time = 60 minutes/job ; rate = 1/60 job/min<BR>\n" );
document.write( "-------------------------------------<BR>\n" );
document.write( "2nd pipe DATA:<BR>\n" );
document.write( "Time = 90 minutes/job ; rate = 1/90 job/min<BR>\n" );
document.write( "-------------------------------------<BR>\n" );
document.write( "Together DATA:<BR>\n" );
document.write( "Time = x minutes/job ; rate = 1/x job/min<BR>\n" );
document.write( "----------------------------------------<BR>\n" );
document.write( "EQUATION:<BR>\n" );
document.write( "rate + rate = together rate<BR>\n" );
document.write( "1/60 + 1/90 = 1/x<BR>\n" );
document.write( "(90+60)/(60*90) = 1/x<BR>\n" );
document.write( "x = 5400/150<BR>\n" );
document.write( "x = 36 minutes (time to do the job together)<BR>\n" );
document.write( "======================================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );